(1) Field of the Invention
The present invention relates to a method for monitoring the manufacture of objects consisting of multiple material layers, such method being applicable, for example, in the production of preformed parts consisting of multiple layers of a material or of wires.
(2) Description of Related Art Including Information Disclosure Under 37 C.F.R. 1.97 and 1.98
There are numerous applications in which parts are produced on an industrial scale from multiple individual layers by successively layering the individual layers or by winding the layers around a winding core, respectively. For example, electric coils are wound from wires and thus successively built layer for layer, rotor blades for wind energy plants in part are also manufactured by winding individual layers of a suitable material onto a basic frame. In all methods, the aim is to obtain, at the end of the manufacturing process, an object having a desired three-dimensional design.
When manufacturing rotor blades for wind energy plants, for example, the proceedings are such that individual layers of a material are wound onto a basic frame, wherein these layers, for example, may consist of resin-soaked fiber-reinforced mats of synthetic material, which, after hardening of the resin, result in a very sturdy preformed body. Thereby, the glass fiber mats are provided on large drums, from which they are reeled off in the course of the production in order to be wound onto the basic frame as individual layers, such that, put in an illustrative manner, the construction is performed similar to applying a plaster bandage. It is important for the safety of the final element that a required minimum material thickness is maintained everywhere at the element, such that the stability of the finished rotor blade is guaranteed.
In the production of electric coils, thus, the winding of the coil wire, the correct construction of the individual layers then is of particular importance, when a high electric voltage drops along the coil wire. Then, with a faulty winding, a voltage difference may occur between two adjacent wire pieces, which is so high that the break-through voltage of the insulation is exceeded, due to which the coil is destroyed when in use. What is important here is, on the one hand, that per applied winding layer there is no deviation from a nominal thickness of the winding layer, thus, this thickness is not exceeded when, for example, two layers cross each other due to faulty winding. On the other hand, also the exact geometrical positioning of the individual wire is of interest in order to prevent the above-described case of the destruction of the coil. In particular, coils are also applied for creating high, precisely-defined magnetic fields in order to enclose, for example, gas plasma within a vacuum by means of the magnetic field created by means of the coils. In such cases, the individual windings of the coils have complicated geometrical shapes, thus, then have to be wound according to an exactly calculated scheme, such that in this utilization case not only the total material thickness of a finished wound coil is of interest, but also the geometrical arrangement of the individual windings, their winding sequence, respectively, is of interest.
A further example, in which products are manufactured on an industrial scale by means of winding techniques, is the production of tires. When building automobile tires, individual rubber layers are wound onto a drum-like carrier, by which successively the finished raw tire is created, which tire may also consist of multiple different rubber compounds. Thereby, air bubbles may form between the individual rubber layers during the winding process; by process faults, for example, when supplying rubber, it may happen that the material thickness of the finished tire locally is too low or too high. A finished produced tire must have a defined local material thickness, thus, have a cross-section following a predetermined profile. With too low material thickness, a tire blow-out may occur; if the material thickness locally is too high, this may lead to undesired running characteristics of the tire, such as, for example, imbalance or radial run-out. In order to prevent the safety risks concomitant with tires manufactured not according to standards, it must be ensured that the tire's cross-section follows the predetermined profile over the entire circumference of the tire.
Testing industrially-made parts, which are manufactured in a laminate or winding technology, according to the state of the art takes place after manufacturing. Thereby, the finished part is examined in respect to its inner construction. To this end, known non-destructive testing procedures, such as, for example, the ultrasound technology or X-raying by means of computer-assisted tomography, are applied.
A huge disadvantage consists in that the testing effort and the expenditure connected thereto, in particular when applying the computer-assisted tomography, are very high and that the test object is examined only after completion, thus, at a point in time when the total manufacturing costs already have occurred. There are also technological limits to the post-finishing testing method, for example, in the case of examination of a coil, it is principally impossible to conclude, after the finishing of the latter, by an imaging method the sequence in which the individual windings have been applied. Also, in part the local resolution, by which a finished object can be reconstructed, is too small to be able to localize small flaws within a compact three-dimensional object.
In particular with automobile tires, there is the problem that it is difficult to discern inclusions within the rubber layers, as in X-rays they show only a very limited contrast difference to the rubber material surrounding them.